Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

B. M. Ravindra ¹, A. S. Janardhan ²

Affiliations
1 Department of Mines and Geology, Kankanadi, Mangalore - 575002, IN
2 Department of Geology, Manasa Gangotri, Mysore - 570006, IN

Abstract

Occurrence of syenite with the mineral assemblages: aegerine-augite-ferroedenite, brownish biotite and mesoperthite is described. From the available data of the associated rocks, it is concluded that the syenite intrusion is late and is associated with major EW linears.

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B. M. Ravindra ¹, B. Krishna Rao ²

Affiliations
1 Geology Division, Tungabhadra Project (CADA), Munirabad 583233, IN
2 Department of Geology, University of Mysore, Mysore 570006, IN

Abstract

A set of longitudinal and transverse faults have been recognised in the coastal tract of Dakshina Kannada district. The coastal faulting and the uplift of Western Ghats are attributed to sea-floor spreading centred on the Mid-Indian Ridge in the Arabian sea. St. Mary dacite eruption during Late Cretaceous must have heralded sea floor spreading in this part of the West Coast. Variations in the coastline and discrepencies in lithology of coastal Dakshina Kannada are explained by lateral movements along transverse faults. The unusual coast-parallel bends of west flowing rivers appear to be guided by longitudinal coastal faults.

Severe sea erosion in Dakshina Kannada was initiated by the increase of pore water pressure in the coast-parallel river bends and blind tributaries, resulting from massive fluvial discharge during monsoon period. The storm waves may have reactivated preexisting longitudinal faults and triggered slumping of the foreshore sea bed in preferential areas of pore water pressure accumulation and with this, destructive sea erosion commenced and it continued till the stumped area in the foreshore bed was filled up by sands brought back by backwash currents.

It is suggested that severe sea erosion in Dakshina Kannada can be controlled effectively by devising suitable canals to release the surplus stream discharge from the coast-parallel river segments and associated blind streams.

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B. M. Ravindra ¹, B. Krishna Rao ², V. N. Vasudev ³

Affiliations
1 Geology Wing, Tungabhadra Project (CADA), Munirabad 583233, IN
2 Geology Department, University of Mysore, Mysore 570006, IN
3 Department of Mines and Geology, Mineral Wing, Bellary 583101, IN

Abstract

Low-grade copper sulphide mineralisation around Kalyadi is localised in an early Precambrian volcanosedimentary suite, characterised by cyclic sedimentational features. The rocks have been intruded by ultramafics, granite and dolerite. The supracrustals have been subjected to three phases of deformation and low-grade metamorphism.

The Fe-Cu sulphide mineralisation is stratiform and stratabound, represented by pyrite. chalcopyrite and pyrrhotite. The salient features of tbe mineralisation suggest that the sulphide ore material derived from volcanic exhalatives was deposited along with their volcanosedimentary host rocks syngenetically about 3.0 b.y. ago. The mineralisation is essentially a sulphide facies of iron-formation. Banded ferruginous quartzite also exists in the area, suggesting consanguineous sulphide-oxide facies relationship. The ore has been deformed and metamorphosed along with the host rocks resulting in mobilisation and moderate enrichment.

Keywords

Economic Geology, Metals, Ore Petrology, Copper, Hassan District, Karnataka.

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B. M. Ravindra ¹, S. N. Nagaraja Sharma ¹

Affiliations
1 Department of Mines and Geology, Khanija Bhavan, 49, Race Course road, Bangalore 560 001, IN

Abstract

Groundwater level data for 1909 and 2004 evince marked but non-uniform groundwater depletion in . southeastern Karnataka. Over the century period, vertical depletion is distinct in the fractured regional aquifer system, mainly in four zones or nadirs. Out of these four, the zone.discharging into Palar basin on the southwest of Kolar schist belt shows widest nadir of groundwater depletion.

Deep mining at Kolar Gold fields over a prolonged period induced deep fractures that facilitated massive migration of groundwater to deeper levels by viscous flow. It is estimated that in deeply fractured zones like KGF, the quantity of groundwater accumulated annually is about 0.4 MCM/km² whereas the average annual rainfall recharge in the average surrounding area is only about 0.09 MCM/km².

The groundwater suction effect in KGF mines and further transfer of groundwater laterally into the highly Fractured discharge zone of low lying river basins, along shear zones and major fractures, appears to be primarily responsible for the severe lowering of groundwater in the region.

Keywords

Groundwater depletion, Induced fractures, Regional groundwater transfer, Kolar region, Karnataka.

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